PHOTOSYNTHESIS GR 11 LIFE SCIENCES
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PHOTOSYNTHESISGR 11 LIFE SCIENCES
Definition:
Photosynthesis is the process where the energy
of the sunlight is used by green plants (and
some animals) to bond molecules together to
form carbohydrates and thus allow the plants
to manufacture their own food
EQUATION
Carbon dioxide + Water + Light Glucose + oxygen
CO2 + H2O C6H12O6 + O2
Chlorophyll
Enzymes
Chlorophyll
Enzymes
TEST FOR PHOTOSYNTHESIS
Experiments to follow:
Test for starch
If light is necessary
If chlorophyll is necessary
If CO2 is necessary
Which gas is released
Reminder
Functions of each
Outer membrane - It is a semi-porous membrane and is permeable to small molecules and ions, which diffuses easily. The outer membrane is not permeable to
larger proteins.
Inner membrane - The inner membrane of the chloroplast forms a border to the
stroma. It regulates passage of materials in and out of the chloroplast. In addition of
regulation activity, the fatty acids, lipids and carotenoids are synthesized in the inner
chloroplast membrane.
Stroma: Stroma is an alkaline, aqueous fluid which is protein rich and is present within
the inner membrane of the chloroplast. The space outside the thylakoid space is
called the stroma. The chloroplast DNA, chloroplast ribosomes and the thylakoid
system, starch granules and many proteins are found floating around the stroma.
Thylakoid SystemThe thylakoid system is suspended in the stroma. The thylakoid system is a collection
of membranous sacks called thylakoids. The chlorophyll is found in the thylakoids and
is the site for the process of light reactions of photosynthesis to happen. The thylakoids
are arranged in stacks known as grana.
Raw materials
Carbon dioxide from the atmosphere
Water from the soil
Radiant energy from the sun
Chlorophyll in the chloroplasts of
green plants
Enzymes
Products
Glucose, which is stored in the
plant as starch
Oxygen, which is released into the
atmosphere.
The process of Photosynthesis
Occurs as a series of complex biochemical processes
Two phases: Light Phase (Light Dependent Phase) and dark phase (Light Independent Phase)
Light and Calvin cycle
1. In the light cycle light falls on the granum of a chloroplast.
2. Chlorophyll molecules inside other granum absorb the light
energy(radiant energy)
3. Some of this energy is used to make energy rich ATP and some is used
to split water molecules into oxygen and energy rich hydrogen atoms
4. In the dark phase ,carbon dioxide, the energy rich ATP and the
energy rich hydrogen atoms are used to make glucose molecules
5. The energy from the energy rich ATP and energy rich hydrogen atoms
is stored in the bonds holding the atoms of the glucose molecule
together
6. So light energy is transferred to energy rich ATP and hydrogen atoms.
The energy in these molecules is then transferred to the bonds in
glucose molecules.
Schematic representation of
process
Light Dependent Stage
The reactions of the light phase take place in the grana of the chloroplast which contain chlorophyll
The chlorophyll molecules absorb light energy
ADP + P(phosphate) = ATP
This energy is used in two ways:
It is used to form the energy carrier ATP(Adenosine Triphosphate)
It is used to split water molecules to release two high- energy hydrogen atoms and oxygen. The oxygen is released into the atmosphere as a by product
Light Independent Stage
Calvin Cycle
The reactions of the dark phase take place in the stroma of the chloroplast (refers to the colorless fluid
surrounding the grana within the chloroplast)
CO2 provides carbon and oxygen, which combine with the high energy hydrogen atoms from the light phase to form carbohydrates such as glucose and starch (Very Quickly)
The high energy hydrogen atoms and the ATP from the light phase provide the energy for this process
All the reactions of the dark phase are controlled by enzymes
Adaptations of chloroplasts for photosynthesis
The double membrane allows water and CO2 to enter easily
The grana contains chlorophyll to trap sunlight
The grana are flat discs with a large surface area
The stroma contain enzymes for reactions of the dark phase
Ribosomes in the stroma synthesize enzymes for photosynthesis
Starch granules are present to temporarily store the starch that is produced
Adaptations of a leaf
Leaf has a large surface area
Leaf is thin
Epidermis is transparent and has no chloroplasts
Stomata are found in the epidermis
Many chloroplasts in the palisade mesophyll cells
Few chloroplasts in the spongy mesophyll cells – large
air spaces
Veins contain xylem and phloem tubes
Importance of photosynthesis
Photosynthesis keeps the oxygen concentration in the
atmosphere and water constant, as oxygen, which is
required by organisms for cell respiration is released
during photosynthesis
Keeps the level of carbon dioxide in the atmosphere
and water constant
Provides food for heterotrophic organisms, as
fats and proteins are also made from the
glucose and starch that are produce during
photosynthesis
Makes chemical energy available for cell
functioning as radiant energy is trapped and
transformed into chemical energy during
photosynthesis so that it can be released during
cellular respiration
Importance of photosynthesis
Factors affecting the rate of photosynthesis
INTERNAL FACTORS
The structure of the leaf
The concentration of products of photosynthesis (if
the starches made are not transported away
quickly they will slow down the rate)
Nature of protoplasm (shortage of water – rate will
be reduced
EXTERNL FACTORS
The CO2 concentration in the atmosphere
A decrease in Carbon dioxide concentration
leads to a decrease in the rate of photosynthesis
An increase in CO2 concentration leads to an
increase in the rate of photosynthesis
Factors affecting the rate of photosynthesis
The intensity of the light
An increase in the light intensity results in an increase in the rate
of photosynthesis, but only to a maximum level.
If the light intensity becomes too high, the stomata close and
carbon dioxide then becomes a limiting factor.
Factors affecting the rate of photosynthesis
The temperature
Plants photosynthesizes optimally at 25◦c
Temperatures that are too high or too low inhibit the
rate of photosynthesis.
At low temperatures enzymes become inactive and
at high temperatures enzymes denature.
At high environmental temperatures, the stomata
close to limit water loss and then carbon dioxide
becomes a limiting factor once again
Factors affecting the rate of photosynthesis
Factors that affect the rate of
photosynthesis
❖ Three important factors namely; light intensity, carbon dioxide concentration and temperature
❖ As the light intensity (brightness of light) increases so the rate of photosynthesis increases
❖ As the carbon concentration increases so the rate of photosynthesis increases
❖ Photosynthesis is controlled by enzymes and enzymes work best at a temperature of 37 degrees Celsius. The temperature should not increase above 37 degree Celsius as enzymes denature at a temperature higher than this.
❖ Photosynthesis will eventually level off and not increase due to the limiting factors
❖ Limiting factors are factors that prevent an increase in the rate of a process such as photosynthesis
❖ In other words even if the light intensity continues increasing there is only so much carbon dioxide available and the temperature is constant.
❖ The carbon dioxide and temperature are, in this case known as limiting factors as all three factors work collaboratively to increase the rate of photosynthesis
❖ An optimum rate of photosynthesis is
ensured by giving the plant as much
light as possible, a high concentration of
carbon dioxide as well as a temperature
of not higher than 37 degrees Celsius
Improving Crop Fields
❖ The greater the rate of
photosynthesis the greater the
productivity of the plant.
❖ The productivity of a plant is
known as how much extra dry
mass (excluding its water
content) it gains over a period of
time
❖ A greater productivity of a plant crop the larger quantity of food to eat.
❖ Plants grown in greenhouses or greenhouse tunnels may grow better then those grown outside. This is because:
❖ The glass roof and walls let lots of light into the greenhouse and trap the heat inside thereby allowing for a high light intensity and a high temperature
❖ Gas cylinders can be used to pump additional carbon dioxide into the greenhouse where it is trapped
❖ Watering is much more efficient within a
greenhouse
❖ The plants do not need to be watered as often as
those outside as transpiration is decreased due to
the increased humidity within the greenhouse.
❖ Insecticides can be sprayed inside the
greenhouse in order to control pests more
effectively.
The role of ATP
❖ ATP (Adenosine Triphosphate) is an energy rich molecule
❖ It is formed when ADP (Adenosine diphosphate) combines with a third phosphate by means of an energy rich bond
❖ This is known as phosphorylation. In other words ADP is phosphorylated.
❖ This reaction is reversible. ATP can be broken down into ADP and a phosphate when an energy rich bond is broken. ATP is dephosphorylated.
❖ The energy from the energy-rich bond is released during this reaction and used in the cell
❖ ATP is an energy carrier in the cell. When a cell needs energy the ATP is broken down into ADP.
❖ The energy released is used for different functions such as:
➢ Synthesis of macromolecules such as nucleic acids, proteins and fats
➢ The contraction of muscle cells
➢ The beating of cillia and flagella.
▪ Cilla (tiny hair like structures – move things over the surface of the cell such as dust particles)
▪ Flagella (longer thread like structures that help cells move through liquid)
➢ Active transport. To move substances from a low concentration gradient to a high concentration gradient
➢ Bioluminescence. The ability of living organisms to give off light through a chemical reaction. For example fireflies and jellyfish glow in the dark
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